When I overlap tracks, they aren't in sync :( help!

I’ll record my guitar, and then try to overlap my voice over the guitar part, but it’s never in sync with each other. How can I fix this?

You’ll want the Time Shift tool for now:

Also, you should be aware that all computers have some latency when recording audio (this is unavoidable).

Newer versions of Audacity have a manually configured latency correction that is easy to set up and quite accurate: